The present invention relates to the preparation of polyelectrolyte membranes carrying charged groups possessing low electrical resistance, superior performance properties and durability. More particularly, the invention relates to a novel method for the production of polyelectrolyte membranes comprising an organic polymer matrix intimately containing a substantial amount of a cross-linked aromatic polymer, and having dissociable functional groups chemically bonded to the aromatic nuclei and to the improved product obtained thereby.
Various ion exchange membranes such as cationic, anionic and bipolar are well known in the art. Styrene-divinylbenzene copolymers with sulfonic acid ion exchange groups (cationic type) are fully disclosed, e.g. in U.S. Pat. No. 2,731,411. The anion-type, for example, a styrene-divinylbenzene vinylpyridine membrane is disclosed in U.S. Pat. No. 2,860,097. Bi-polar membranes based on polyethylene-styrene copolymers are also known, e.g. U.S. Pat. Nos. 3,372,101, 3,388,080 and 3,562,139. Such membranes generally have the disadvantage of relatively high electrical resistance and low current efficiency. Heretofore, in accordance with teachings of the prior art it has been extremely difficult to obtain polyelectrolyte membranes with a relatively high number of cross-linking bonds, high functional group concentrations and yet have low electrical resistance and long operational capabilities. The present invention discloses a novel method to obtain a product with these advantages.